Variable resistance element with spaced rows of parallel tabs

ABSTRACT

A resistance element for a variable resistance control having a plurality of spaced commutator bars disposed on opposite sides of a resistance film, each of the commutator bars in one row being in straddled relationship to the bars in the other row and at least the ends of the commutator bars being in overlapping relationship with a resistance film. A movable contactor mounted for movement along a predetermined path transversely of the commutator bars engages the commutator bars for altering the resistance of the variable resistance control.

United States Patent lnventors Herbert H. Leerkamp Berue;

Daniel C. Kinsey, Decatur, both of Ind. 53,226

July 8, 1970 Oct. 12, 1971 CTS Corporation Elkhart, Ind.

App]. No. Filed Patented Assignee VARIABLE RESISTANCE ELEMENT WITH SPACED ROWS OF PARALLEL TABS 11 Claims, 6 Drawing Figs.

U.S.Cl 338/194, 338/95, 338/126, 338/186, 338/190 Int. Cl 1101c 9/04 Field of Search 338/92, 95, 125,126,128,l55,171,185,186,188,l90, 194, 308

I he i 5 [56] References Cited UNITED STATES PATENTS 2,662,147 12 1953 Wilentchik 338 190 x 2,688,679 9 1954 Schleuning 338 190 2,890,431 6/1959 Cobb 338/95 x Primary ExaminerLewis H. Myers Assistant Examiner-Gerald P. Tolin Attorney-John J. Gaydos 19, 19 lea/5.1

III

PATENTEU B 2 l9?! 3,613,042

URE- 3 FIGURE- 4 FIGURE-6 FIGURE-5 mvzm'ons' I HERBERT H. LEERKAMP DANIEL C. KINSEY ATTORNEY VARIABLE RESISTANCE ELEMENT WITH SPACED ROWS OF PARALLEL TABS The present invention relates to a variable resistance control and, more particularly, to a variable resistance element for a variable resistance control or potentiometer.

' In certain applications employing variable resistance controls, it is desirable that the equivalent noise ratio (E.N.R.) be maintained below a specified minimum percentage. It is generally well known that a variable resistance control having a wirewound resistance element has a lower E.N.R. than a control having a film-type resistance element. Accordingly wirewound variable resistance controls are usually specified for use in an electronic circuit when a low E.N.R. is desirable. Wirewound variable resistance controls can be manufactured without much difficulty when low-resistance values are specified. With the present trend, however, toward miniaturization there is an increased demand for higher resistivities. This causes difficulties to occur since a higher resistivity can only be obtained with a smaller diameter wire. It is well known that the E.N.R. of the film-type variable resistance element can be decreased by embedding a plurality of spaced commutator bars below the resistance path and having one end of each commutator bar extending transversely beyond the edge of the resistance path for engagement with a movable contact (see Pritikin et al. U.S. Pat. No. 2,632,831). Obviously the series of spaced commutator bars can comprise a segmented low-resistance path such as shown in Schleuning U.S. Pat. No. 2,688,679. By having the movable'contact engage the spaced commutator bars instead of the resistance element, the E.N.R.

is decreased. Although Pritikin et al. were primarily interested in decreasing the source of noise, Schleuning was primarily interested in precisely adjusting with great accuracy the resistance value between adjacent commutator bars. Although such prior art variable resistance elements are satisfactory for maintaining a low E.N.R., it would be desirable to provide improved resistanceelements and to decrease by 50 percent the change in resistance when a movable contact moves from one commutator bar to another.

Accordingly it is an object of the present invention to provide an improved variable resistance element having a plurality of commutator bars extending transversely from opposite sides of an elongated resistance film, the bars on one side of the film being in staggered relationship to the bars on the opposite side of the resistance film. Another object of the present invention is to provide an improved variable resistance element having two rows of spaced commutator bars disposed on a surface of a dielectric substrate and resistance segments interconnecting the bars in each row. An additional object of the present invention is to provide an improved variable resistance element wherein a contactor having a pair of spaced contacts is mounted for movement along a pair of predetermined paths extending substantially transversely along two rows of spaced commutator bars with the ends of the bars in overlapping relationship to an elongated resistance film disposed between the two rows on a dielectric base. A further object of the present invention is to provide a variable resistance element having two rows of spaced commutator bars disposed on a surface of a dielectric substrate and resistance segments interconnecting the bars in each row with the bars projecting above the surface of the substrate more than the resistance segments. Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features of novelty characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Briefly, the present invention is concerned with variable resistance elements comprising a dielectric substrate having disposed thereon two rows of spaced commutator bars arranged to define a pair of paths extending substantially transversely of the bars. A contactor having a pair of contacts is mounted for movement along the pair of paths defined by the commutator bars. A plurality of resistance segments interconnect the commutator bars in each row together. Terminating pads electrically connect the two rows of commutator bars in parallel. In a preferred embodiment of the present invention, a resistance film is disposed on the surface of the substrate between the two rows of bars and electrically interconnects the bars and the resistance segments in the two rows together. Preferably the commutator bars extend above the surface of the substrate beyond the resistance segments. Lead wires preferably anchored in square holes provided in the dielectric substrate are electrically connected to the terminating pads electrically connecting the resistancefilm, the two rows of commutator bars and the resistance segments in parallel.

For a better understanding of the present invention reference may be had to the accompanying drawings wherein the same reference numerals have been applied to like parts and wherein:

FIG. 1 is a side view of one form of a variable resistance control in which the resistance element of the present invention is employed;

FIG. 2 is a sectional view taken along lines II-Il of FIG. 1;

FIG. 3 is a top plan view of the resistance element built in accord with the present invention and shown in FIGS. 1 and 2;

FIG. 4 is a sectional view taken along lines IV-IV of FIG. 3;

FIG. 5 is a top plan view of a modification of a resistance element built in accord with the present invention; and

FIG. 6 is a grossly enlarged fragmentary section taken along lines Vl-VI of FIG. 3.

Referring now to the drawings, the variable resistance element 10 can be employed with many different types of variable resistance controls such as the control 11 shown in FIG. 1 of the drawings. Generally such variable resistance controls comprise a housing 12 supporting the variable resistance element 10. A contactor 13 mounted for movement in the housing engages the variable resistance element 10 intermediate the ends thereof. A movable contactor generally engages a resistance element with a rocking, wiping or rolling motion. When a contactor having a rocking motion such as shown in FIG. 1 is employed, a downward force applied against an actuating member 14 engaging one end of the contactor 13 causes the contactor to rock to the right advancing engagement of the contactor with the commutator bars and altering the resistance of the variable resistance control.

Considering more specifically the variable resistance element 10, it comprises a dielectric base or substrate of suitable material such as ceramic laminated fiber or plastic. The thickness of the substrate should be sufficient to prevent deflection thereof when engaged by a rocker-type contactor or the substrate should be adequately supported in the housing. When high-temperature resistance elements are specified, a ceramic dielectric substrate of alumina or steatite is preferable.

According to the present invention, two rows l6, 17 of spaced commutator bars 16a and 1741 are disposed on a surface 15a of the dielectric substrate 15. The commutator bars are formed in a suitable manner, e.g., by screening a gold or platinum-gold alloy conductive paste onto the surface of a substrate 15 and firing the substrate containing the screened commutator bars to fuse the bars to the surface of the substrate. Preferably the commutator bars in one row 16 are in staggered relationship to the commutator bars in the other row 17 when a small incremental change in resistance value is desired as the contactor is moved from one end of the resistance element 10 to the other, e.g., each of the commutator bars in row 16 lies in a plane disposed between a pair of commutator bars in row 17. Simultaneously with the screening of the commutator bars 160 and 17a onto the surface of the substrate, a pair of terminating pads 18 are also screened onto the surface of the substrate 15 at opposite ends thereof.

Whenever high resistance values are desired, a long narrow resistance film 19 is deposed on the surface 150 of the sub strate in overlapping relationship with the inner ends of the commutator bars 16a and 17a as best shown in FIG. 3 of the drawings. The depositing of the resistance film onto a surface of the substrate is well known in the art and need not be described in detail here. Attention is directed to Faber, Sr. et al. U.S. Pat. No. 3,304,l99 for a more detailed disclosure of one of the many satisfactory resistance materials that can be screened on a surface of a ceramic substrate and fired to produce the resistance film 19.

For the purpose of connecting the resistance element to an electrical circuit, the substrate is preferably provided with a pair of square tapered holes 20 adapted to receive a pair of lead wires 21 having a cylindrical cross section. The sides of the square hole engage the lead wire as it is forced into the hole and anchored. Solder, conductive epoxy or other suitable terminating material 22 is employed for electrically connecting the lead wires to the terminating pads.

The contactor 13 provided with a pair of spaced contacts 13a and 1311 (see FIG. 2) is mounted for movement in the housing 12 for electrically engaging the commutator bars along a pair of paths 23 and 24 extending substantially transversely of the bars 16a and 17a. As the contactor 13 moves intermediate the ends of the resistance element 10, the source of noise or E.N.R. is decreased considerably since the contacts do not directly engage the resistance film but instead engage the commutator bars containing a high metal content. By positioning the commutator bars in one row 16 in staggered rela-' tionship to the other row 17, the incremental change in resistance is decreased since the contactor 13 will alternately engage or disengage commutator bars on opposite sides of the resistance film.

As is well known the value of the total resistance of the resistance film intermediate the terminating pads can be decreased by widening the resistance film or a nonlinear resistance can be obtained by tapering the resistance film. in accord with the present invention and to assure that the contacts 13a, 13b do not directly engage the resistance film when the film overlies or extends a distance beyond the outer ends'of the commutator bars of either one or both of the rows 16 and 17, the commutator bars 16a, as best shown in FIG. 6, extend above the surface 154 of the substrate 15 beyond the resistance film 19 or segments 19a disposed between adjacent commutator bars. If the thickness of the bars is equal to the film then two layers of the conductive paste are applied on the surface 15a to form the commutator bars 16a and 17a. Also, the resistance film can be screened onto the surface 15a before the commutator bars to assure that the bars project above the film. Moreover if the bars are screened and fired before the film, the film can be screened over the bars giving the bars a greater projection. It has been observed that when the resistance film is screened over the bars the conductive material in the bars projects through the film shorting a portion of the film and causing the film to become a low-resistance commutator bar.

In some forms of the invention it may be desirable to adjust the resistance value of the element 10. Accordingly in another embodiment of the present invention (see FIG. 5), two spaced parallel resistance films 119 are applied along the inner ends of the commutator bars. Each resistance film 119 comprises a plurality of resistance segments 119a interconnecting the spaced commutator bars in each row together and a narrow elongated resistance film 11%. The resistance values between the lead wires 121 can be increased by removing a portion of the film along the inner edges of the resistance film 11%.

Although the resistance element 10 of the present invention is disclosed for use with a rectilinear contactor, it is to be understood that the resistance element can be arranged in an arcuate form for engagement with a rotary contactor. Generally the conductive bars 16a and 17a and the terminating pads 18 are deposited and bonded to the substrate by firing before the resistance film is deposited on the substrate. Such procedure decreases thedelivery or manufacturing time of the resistance element 10 to a customer since partly prefinished substrates with the commutator bars and terminating pads can be stored and made immediately available to manufacturing for applying the proper resistance film onto the substrate.

Preferably the commutator bars are equally spaced and normal to the predetermined path of the contactor. A nonlinear characteristic of the resistance element can be readily obtained by varying the relative spacing of or width between the commutator bars. Also instead of applying the commutator bars and resistance film onto a flat surface whether straight or arcuate, the commutator bars, resistance film and segments can also be applied onto the surface of a cylindrical substrate in the form of a helix. Furthermore, although a pair of spaced contacts 13a 13b are shown in the drawings, it is tobe understood that a plurality of contacts or fingers can engage each row of commutator bars;

While there has been illustrated and described what is at present considered to be a preferred embodiment of the present invention and an additional modification thereof, it will be appreciated that numerous changes and modifications are likely to occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In a variable resistance control the combination of a dielectric substrate, a first plurality of spaced commutator bars disposed on a surface of said substrate and arranged to define a first path extending substantially transversely of said bars, a second plurality of spaced commutator bars disposed on said surface and arranged to define a second path substantially transversely of said second plurality of spaced commutator bars, the first plurality of spaced commutator bars being spaced from and in staggered relationship to the second plurality of spaced commutator bars, the first and second path being in spaced parallel relationship, a first plurality of resistance segments electrically interconnecting the first plurality of spaced commutator bars and a second plurality of resistance segments electrically interconnecting the second plurality of spaced commutator bars, a contactor having a pair of spaced contacts mounted for movement along the first and second paths, and terminating means connected to the first and second plurality of spaced commutator bars and to the contactor.

2. The variable resistance control of claim I, wherein the first path is spaced from the first plurality of resistance segments, and the second path is spaced from the second plurality of resistance segments.

3. The variable resistance control of claim 1, wherein the commutator bars extend above the surface of the substrate beyond the resistance segments.

4. The variable resistance control of claim 1, wherein a resistance film disposed on the surface of the substrate electri cally connects the first and second pluralities of resistance segments together.

5. The variable resistance control of claim I, wherein the commutator bars are equally spaced and normal to the first and second paths.

6. The variable resistance control of claim 1, wherein the terminating means comprises a pair of terminating pads electrically connecting the first and second pluralities of resistance segments in parallel, the substrate is provided with a pair of square holes, a lead wire is anchored in each of the square holes, and means electrically connects the lead wires to the pads.

7. A variable resistance control comprising a substrate of dielectric material, a resistance film secured to a surface of the substrate, a plurality of spaced commutator bars disposed on the substrate on both sides of the resistance film, each of the commutator bars having a portion thereof in overlapping relationship with the resistance film, some of the commutator bars on one side of the resistance film being in staggered relationship to the commutator bars on the other side of the resistance film, a movable contactor having a contact mounted for movement along a predetermined path transversely of and in en- .gagement with the commutator bars on both sides of the releast an end of each of the commutator bars is in overlapping relationship with the resistance film.

9. The variable resistance control of claim 7, wherein the commutator bars extend transversely of the resistance film.

10. The variable resistance control of claim 7, wherein the contactor comprises a pair of spaced contacts engageable with the commutator bars.

11. The variable resistance control of claim 7, wherein the commutator bars are equally spaced. 

1. In a variable resistance control the combination of a dielectric substrate, a first plurality of spaced commutator bars disposed on a surface of said substrate and arranged to define a first path extending substantially transversely of said bars, a second plurality of spaced commutator bars disposed on said surface and arranged to define a second path substantially transversely of said second plurality of spaced commutator bars, the first plurality of spaced commutator bars being spaced from and in staggered relationship to the second plurality of spaced commutator bars, the first and second path being in spaced parallel relationship, a first plurality of resistance segments electrically interconnecting the first plurality of spaced commutator bars and a second plurality of resistance segments electrically interconnecting the second plurality of spaced commutator bars, a contactor having a pair of spaced contacts mounted for movement along the first and second paths, and terminating means connected to the first and second plurality of spaced commutator bars and to the contactor.
 2. The variable resistance control of claim 1, wherein the first path is spaced from the first plurality of resistance segments, and the second path is spaced from the second plurality of resistance segments.
 3. The variable resistance control of claim 1, wherein the commutator bars extend above the surface of the substrate beyond the resistance segments.
 4. The variable resistance control of claim 1, wherein a resistance film disposed on the surface of the substrate electrically connects the first and second pluralities of resistance segments together.
 5. The variable resistance control of claim 1, wherein the commutator bars are equally spaced and normal to the first and second paths.
 6. The variable resistance control of claim 1, wherein the terminating means comprises a pair of terminating pads electrically connecting the first and second pluralities of resistance segments in parallel, the substrate is provided with a pair of square holes, a lead wire is anchored in each of the square holes, and means electrically connects the lead wires to the pads.
 7. A variable resistance control comprising a substrate of dielectric material, a resistance film secured to a surface of the substrate, a plurality of spaced commutator bars disposed on the substrate on both sides of the resistance film, each of the commutator bars having a portion thereof in overlapping relationship with the resistance film, some of the commutator bars on one side of the resistance film being in staggered relationship to the commutator bars on the other side of the resistance film, a movable contactor having a contact mounted for movement along a predetermined path transversely of and in engagement with the commutator bars on both sides of the resistance film, and terminating means connected to the resistance film and to the contactor.
 8. The variable resistance control of claim 7, wherein at least an end of each of the commutator bars is in overlapping relationship with the resistance film.
 9. The variable resistance control of claim 7, wherein the commutator bars extend transversely of the resistance film.
 10. The variable resistance control of claim 7, wherein the contactor comprises a pair of spaced contacts engageable with the commutator bars.
 11. The variable resistance control of claim 7, wherein the commutator bars are equally spaced. 